Methods and apparatus for identifying audio/video content using temporal signal characteristics

ABSTRACT

Methods and apparatus for identifying audio/video content using temporal characteristics of a signal are disclosed. The disclosed apparatus and methods receive a signature associated with audio/video content presented at a monitored site, wherein the signature is based on a plurality of time intervals associated with audio features of the audio/video content presented at the monitored site and identify the audio/video content presented at the monitored site based on the received signature.

RELATED APPLICATIONS

This application is a continuation U.S. patent application Ser. No.11/404,276, entitled “METHODS AND APPARATUS FOR IDENTIFYING AUDIO/VIDEOCONTENT USING TEMPORAL SIGNAL CHARACTERISTICS” and filed on Apr. 14,2006, which is a continuation of PCT Patent Application Serial No.PCT/US2004/018205, entitled “METHODS AND APPARATUS FOR IDENTIFYINGAUDIO/VIDEO CONTENT USING TEMPORAL SIGNAL CHARACTERISTICS” and filed onJun. 8, 2004, which claims priority from U.S. Provisional PatentApplication No. 60/512,507, entitled “METHODS AND APPARATUS FORIDENTIFYING AUDIO/VIDEO CONTENT USING TEMPORAL CHARACTERISTICS OF AUDIOFEATURES” and filed on Oct. 17, 2003, the entire disclosure of which isincorporated by reference herein in its entirety. This applicationcontains subject matter related to that disclosed in U.S. ProvisionalPatent Application No. 60/511,838, entitled “AUDIO SIGNATURE APPARATUSAND METHODS,” the disclosure of which is incorporated by referenceherein in its entirety. Additionally, this application contains subjectmatter related to that disclosed in International Patent Application No.PCT/US04/10562, entitled “AUDIO SIGNATURE APPARATUS AND METHODS,” thedisclosure of which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to identifying audio/videocontent and, more specifically, to methods and apparatus for identifyingaudio/video content using temporal signal characteristics.

BACKGROUND

The metering of audio/video content (e.g., television programs, radioprograms, etc.) is typically performed by collecting consumption records(e.g., viewing records) or other consumption information from a group ofstatistically selected households. These viewing records are typicallygenerated by identifying the audio/video content displayed in thesehouseholds.

Some techniques for identifying displayed audio/video content are basedon the use of audio and/or video signatures. In general, signature-basedaudio/video content identification techniques use one or morecharacteristics of presented (but not yet identified) audio/videocontent to generate a substantially unique signature (e.g., a series ofdigital values, a waveform, etc.) for that content. The signatureinformation for the content being presented or rendered is thentypically compared to signature information generated for knownaudio/video content. When a substantial match is found, the audio/videocontent can, with a relatively high probability, be identified as theknown audio/video content having substantially matching signatureinformation.

Although the use of signatures to identify consumed audio/video contentis growing, known computationally efficient signature-based programidentification techniques are not sufficiently reliable because theseknown techniques typically ignore important distinguishingcharacteristics of the audio/video signal. As a result, such knowntechniques may limit or prevent the identification of audio/videocontent and/or may result in an incorrect identification of thatcontent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example system within which theaudio/video content identification apparatus and methods describedherein may be implemented.

FIG. 2 is a block diagram of an example manner in which the monitoredsite of FIG. 1 may be implemented.

FIG. 3 is a flow diagram depicting an example manner in which theexample monitored site of FIG. 2 may be configured to generate andcollect signatures.

FIG. 4 is a block diagram depicting an example manner in which the audiosignature processor of FIG. 2 may be implemented.

FIG. 5 is a flow diagram that generally depicts an example manner inwhich the audio signature processor of FIG. 4 may be configured togenerate and process audio signatures.

FIG. 6 is a flow diagram depicting an example manner in which theaudio/video content selector of FIG. 4 may be configured.

FIG. 7 is a more detailed flow diagram depicting an example manner inwhich the signature generators of FIG. 4 may be configured to generateaudio signatures.

FIG. 8 is a graph depicting an example audio signal that may beprocessed by the example audio signature processor of FIG. 2.

FIG. 9 is a block diagram depicting another example manner in which theaudio signature processor of FIG. 2 may be implemented.

FIG. 10 is a block diagram depicting an example manner in which theaudio signature generators of FIG. 4 may be implemented.

FIG. 11 is a flow diagram depicting an example manner in which theapparatus of FIG. 10 may be configured to generate audio signatures.

FIG. 12 is a flow diagram depicting an example manner in which theapparatus of FIG. 10 may be configured to generate smoothed data.

FIG. 13 is an example graph depicting smoothed data generated by theapparatus of FIG. 10.

FIG. 14 is a flow diagram depicting an example manner in which thesignature comparator of FIG. 4 and/or the central processing facility ofFIG. 1 may be configured to compare signatures.

DETAILED DESCRIPTION

For purposes of clarity, the following discussion describes methods andapparatus for identifying audio/video content using temporalcharacteristics of an audio signal. However, the methods and apparatusdescribed herein may be extended and/or modified to use temporalcharacteristics of any signal associated with the audio/video content.For example, temporal characteristics of a video signal and/or a digitalsignal may be used instead of the example audio signal described herein.

FIG. 1 is a block diagram of an example system 100 within which theaudio/video content identification apparatus and methods describedherein may be implemented. The example system 100 shown in FIG. 1includes a content delivery/distribution system 102 that receives videoand/or audio content from a plurality of audio/video content providers104 and 106. The content delivery/distribution system 102 may be anyform of audio and/or video content delivery/distribution system. Forexample, the content delivery/distribution system 102 may include aradio broadcast station, a television broadcast station, apoint-to-point network, a multipoint network, etc. The audio/videocontent providers 104 and 106 may provide media content such astelevision programs, advertisements, audio (e.g., radio) programs, stillimage information (e.g., web pages), etc. in known manners to thecontent delivery/distribution system 102. The contentdelivery/distribution system 102 may transmit one or more media signalscontaining digital and/or analog audio/video content information to areference site 108 and at least one monitored site 110 via respectivecommunication paths or links 112 and 114.

The communication paths or links 112 and 114 may include any combinationof hardwired or wireless links such as, for example, satellite links,wireless land-based links, cable links, the Internet, etc. The signalsconveyed via the links 112 and 114 may contain multi-program analogsignals and/or digital data streams, which are commonly employed withexisting broadcast systems as well as other types of audio/video contentdelivery/distribution systems.

As shown in FIG. 1, the reference site 108 may include a plurality ofreceivers (e.g., set-top boxes or the like) 116, 118 and 120 thatsimultaneously demodulate, demultiplex and/or decode audio, video and/orother information received via the communication link 112 from thecontent delivery/distribution system 102. In one example, each of thereceivers 116, 118 and 120 receives audio information associated with adifferent portion of the audio/video content (e.g., a different program)that is currently being transmitted (e.g., broadcast) and provides theaudio information to a reference site processor 122. For example, thereceiver 116 may provide audio information associated with a firstprogram while the receivers 118 and 120 provide audio informationassociated with respective second and third programs. In any case, thereference site processor 122 is configured to control and/or hasinformation indicating to which portion of the audio/video content(e.g., which channel, program, etc.) conveyed via the link 112 each ofthe receivers 116, 118 and 120 is currently tuned.

In general, the reference site processor 122 includes the apparatus andmethods described herein for collecting or generating referencesignature information for a plurality of simultaneously broadcastprograms. The reference site processor 122 sends the generated orcollected reference signature information to a central processingfacility 124 via a communication link 126. In turn, the centralprocessing facility 124 may store the reference signature information ina database 130 and, as described in greater detail below, may processthe reference signature information together with information receivedfrom the reference site processor 122 to generate information related tothe consumption of audio/video content.

The monitored site 110 could be, for example, a statistically selectedhome, business, etc. containing a television, a radio, a computer, etc.However, it should be recognized that, while the monitored site 110 isdepicted in FIG. 1 as receiving audio/video content from a remotelysituated content delivery/distribution system 102 (e.g., a broadcaststation) via the communication link 114, the monitored site 110 mayalternatively or additionally receive audio/video content from one ormore local audio/video content delivery systems or devices 128. Thelocal sources 128 may include one or more DVRs, DVD players, VCRs, etc.In addition, while the example system 100 shown in FIG. 1 depicts asingle monitored site (i.e., the monitored site 110), multiple monitoredsites may receive audio/video content via the link 114 and may becommunicatively coupled to the central processing facility 124.

FIG. 2 is a block diagram of an example system 200 that may be used toimplement the monitored site 110 of FIG. 1. As shown in FIG. 2, theexample system 200 includes a media delivery, presentation or outputdevice 202 such as, for example, a television or a video monitor thatreceives an audio/video content signal 203, which may be deriveddirectly or indirectly via the communication link 114 (FIG. 1). Forexample, the audio/video content signal 203 may be provided by a lownoise block coupled to a satellite receiving dish in the case where thelink 114 (FIG. 1) is a satellite communication link. A receiver, decoderor set-top box 204 may be serially imposed between the audio/videocontent signal 203 received via the link 114 and the output device 202.For example, in the case where the audio/video content signal 203received via the link 114 is a digital satellite or cable televisiontransmission, the set-top box 204 demodulates the broadcast signal,demodulates multi-program data streams and selectively parses videoand/or audio data packets associated with a desired channel and/orprogram. The selected data packets are processed to form an outputsignal 206 that can be processed and output (e.g., played, displayed, orotherwise presented) by the output device 202. For example, in the casewhere the output device 202 is a television, the output signal 206 maybe a composite video signal, an S-video signal, a red, green, blue (RGB)signal, or any other displayable or renderable video signal applied tothe appropriate input(s) of the output device 202. In the case where theaudio/video content signal 203 received via the link 114 is aconventional analog television transmission or signal, the set-top box204 may not be required and the audio/video content signal 203 may bedirectly coupled to the output device 202 (e.g., directly coupled toUHF/VHF inputs). In addition to signal processing functions, the set-topbox 204 may also perform access control functions such as, for example,determining the audio/video content to which a user of the examplesystem 200 is permitted access to based on subscription status orsubscription information associated with the example system 200,generating displayable program guide information, etc.

The example system 200 also includes an audio signature processor 208that may be configured to perform audio signature collection orgeneration, comparison and/or signature match detection functions toidentify the audio/video content (e.g., what channel, program, etc.)presented or delivered by the output device 202. More specifically, theaudio signature processor 208 receives the audio/video content signal203 and an audio output signal 210, which may be provided directly bythe output device 202. The audio output signal 210 contains audioinformation associated with the audio/video content currently consumedvia or presented by the output device 202. For example, in the casewhere the audio/video content signal 203 received via the link 114 isdelivered via a broadcast signal, the audio information provided by theaudio output signal 210 may be associated with a television channel orprogram to which the example system 200 is currently tuned.Alternatively, the audio signature processor 208 may be coupled to anacoustic transducer 212 such as, for example, a microphone that isproximate to an acoustic output device (e.g., a speaker) associated withthe output device 202. In that case, the acoustic transducer 212supplies an audio output signal 214 containing information associatedwith the audio/video content currently presented by the output device202 instead of, or in addition to, the audio output signal 210.

As described in greater detail below, the audio signature processor 208generates audio/video content signature information, and may alsocollect or generate reference signature information from the audio/videocontent signal 203 received via the link 114. In some examples, theaudio signature processor 208 sequentially generates referencesignatures for programs, channels or, more generally, audio/videocontent extracted or otherwise derived from the audio/video contentsignal 203 and compares the reference signatures to the signatureinformation associated with the audio/video content currently beingconsumed via the output device 202. If the comparison of referencesignature information to the signature information associated with theaudio/video content currently being consumed yields at least asubstantial match, the audio signature processor 208 may identify theaudio/video content currently being consumed as the audio/video content(e.g., the channel or program) associated with the reference signatureinformation to which the currently viewed audio/video content signatureinformation substantially matched.

The audio signature processor 208 is coupled to a site unit 218 via acommunication link or connection 220. The audio signature processor 208periodically or continuously sends consumption information (e.g.,audio/video content, channel and/or program information) associated withaudio/video content presented by or consumed via the output device 202to the site unit 218. In turn, the site unit 218 processes theconsumption information it receives from the audio signature processor208 and sends, for example, consumption records or information to acentral facility such as, for example, the central processing facility124 of FIG. 1, via a communication link 222. The communication link 222may include one or more wireless communication links (e.g., cellular,satellite, etc.), hardwired communication links (e.g., phone lines), orany other combination of communication hardware and technology platformsthat employ any desired combination of communication protocols.

While FIG. 2 depicts the audio signature processor 208 as being locatedat a monitored site, some or all of the functions of the audio signatureprocessor 208 can be distributed among a plurality of physicallocations. For instance, as discussed in greater detail in connectionwith the example system shown in FIG. 4 below, the reference signaturegeneration function, the signature comparison function and/or thesignature match detection function may be performed by differentphysical systems, some or all of which may be located in differentphysical locations.

FIG. 3 is a flow diagram that depicts an example manner in which theexample monitored site 200 of FIG. 2 may be configured to generate andcollect signatures. Initially, the audio signature processor 208 (FIG.2) obtains (e.g., generates, collects, etc.) signatures or signatureinformation from a plurality of signals (e.g., the audio output signals210 and/or 214, and the reference signal 203) (block 302). As describedin greater detail in connection with FIG. 5 below, the signatures outputby the audio signature processor 208 (FIG. 2) are sent to the site unit218 (FIG. 2) via the communication link or connection 220 (FIG. 2). Thesite unit 218 adds the signatures, received from the audio signatureprocessor 208, to a collection of signatures (block 304). Such acollection of signatures may be implemented using a database file, atext file, a serialized data structure, or one (or any combination) ofmany well-known data storage mechanisms or techniques. The signaturesstored in the collection may be time stamped and stored along with otherconsumption information such as, for example, channel numbers, programidentification information, etc.

If the site unit 218 (FIG. 2) determines that all the requiredsignatures have not been collected (block 306), the site unit 218 (FIG.2) returns control to the audio signature processor 208 (FIG. 2) andwaits for the additional signatures to be obtained (block 302). On theother hand, if the site unit 218 (FIG. 2) determines that all requiredsignatures have been collected (block 306), the site unit 218 (FIG. 2)sends the collection of signatures to the central processing facility124 (FIG. 1) via the link 222 (FIG. 2) (block 308). The site unit 218(FIG. 2) may determine at block 306 whether all signatures have beencollected by using a time limit, such as a number of minutes, hours,days, weeks, months, etc, to delimit when all signatures that have beencollected are ready to be sent to the central processing facility 124.After sending the collection of signatures at block 308, the site unit218 (FIG. 2) may return control to block 302 and continue to obtainadditional signatures.

While FIG. 3 depicts an example manner by which signatures are collectedor generated for a period of time and then sent in groups to the centralprocessing facility 124 (FIG. 1), other manners of conveying signatureinformation to the central processing facility 124 (FIG. 1) may be usedinstead. For example, signatures may be collected and conveyed to thecentral processing facility 124 (FIG. 1) on a continuous basis (e.g., ona streaming basis) rather than in groups sent on a periodic basis.However any other suitable manner of conveying signatures may be usedinstead. Additionally, as noted above in connection with FIG. 1, thecentral facility 124 (FIG. 1) may perform statistical analyses using thecollected signatures to derive audio/video content consumption behaviorinformation, or any other desired information, therefrom.

FIG. 4 is a more detailed block diagram that depicts an example mannerin which the audio signature processor 208 shown in FIG. 2 may beimplemented. The example audio signature processor 400 of FIG. 4includes an audio/video content selector 402 (e.g., a scanning tuner)that receives the audio/video content signal 203 (e.g., the referencesignal), which may contain a plurality of channels and audio and/orvideo programs available for consumption (e.g., viewing, listening,etc.), and selects a portion of the audio/video content containedtherein (e.g., a channel, program, etc.) for further processing. Inparticular, in the case where the audio/video content signal 203 is amulti-program analog signal, the audio/video content selector 402 mayvary a demodulator mixing frequency to selectively tune to particularchannels and programs. On the other hand, if the audio/video contentsignal 203 is a multi-program digital data stream, the audio/videocontent selector 402 may include digital receiver functions thatdemodulate, demultiplex and selectively parse the data stream to extractaudio and/or video data packets associated with particular channels orprograms. In either case, the techniques for processing suchmulti-program analog signals and digital signals are well known and,thus, are not described in greater detail herein.

In general, the audio/video content selection process performed by theaudio/video content selector 402 results in the sequential generation ofsignature information for a plurality of channels and/or audio/videoprograms. Also, generally, the audio/video content selection process (asdescribed in greater detail below in connection with FIG. 5) continuesuntil the audio signature processor 400 determines that a substantialmatch has been identified (i.e., that the audio/video content currentlybeing consumed via the output device 202 (FIG. 2) can be identified witha relatively high degree of certainty), or until the audio signatureprocessor 400 determines that a substantial match cannot be identified(e.g., all available audio/video content has been selected, processed toform audio signatures and none of those audio signatures substantiallymatches the signature information of the audio/video content currentlybeing consumed). In one example, the audio/video content selectionperformed by the audio/video content selector 402 may be based on apredetermined numerical sequence (e.g., a sequence of channel numbers orprogram numbers). In another example, the audio/video content selectionmay be based on a probability of matching. For example, the audio/videocontent selector 402 may select channels associated with recentlyconsumed audio/video content. Additionally or alternatively, theaudio/video content selector 402 may select channels based on thehistorical frequency with which audio/video content has been consumedvia those channels.

The audio/video content selector 402 outputs an audio/video contentsignal 404 to a signature generator 406. The audio/video content signal404 contains audio information associated with the audio/video contentcurrently selected by the audio/video content selector 402. Thesignature generator 406 processes the received audio information togenerate audio signature information therefrom. As described in greaterdetail below, the signature generator 406 uses one or morecharacteristics (e.g., temporal characteristics) of one or more audiofeatures of the signal 404 to generate signatures or signatureinformation. For example, the signature generator 406 may use the amountof time between the peak signal magnitudes above or below apredetermined threshold, the amount of time between signal zerocrossings, the temporal characteristics of signal wavelets, the temporalcharacteristics of signal spectral content, or any other features orcharacteristics of the signal 404. Regardless of the particularcharacteristics or audio features used by the signature generator 406 togenerate signatures or signature information, the resulting signaturesare substantially uniquely characteristic of the audio/video contentcontained within the signal 404 and, thus, may be used as a reference tocompare the audio/video content currently selected by the audio/videocontent selector 402 to the audio/video content currently being consumedby an audience member (e.g., via the consumption signals 210 and 214).

A second signature generator 408 receives an audio output signal fromthe output device 202 (FIG. 2) (e.g., the audio output signal 210 or,alternatively, the signal 214 from the acoustic transducer 212). Asdescribed above, the signals 210 and 214 are associated with orrepresentative of the audio/video content being presented by or consumedvia the output device 202. The signature generator 408 is substantiallythe same or identical to the signature generator 406 and, thus,generates audio signatures or information in a substantially similar oridentical manner to that of the signature generator 406.

As described in greater detail below in connection with FIG. 10, thesignature generators 406 and 408 may each include a smoothing functionto reduce or eliminate noise, spurious data, etc., thereby facilitatingthe matching of signature information derived from the same audio/videocontent delivered via different signal paths (e.g., via an output deviceaudio output and the reference signal).

The time stamper 410 may be configured to provide time stamps that areused by the signature generators 406 and 408 to time stamp signaturedata generated thereby. For example, each signature may have one or moretime stamps associated therewith to facilitate subsequent signaturecomparison operations, correlation operations, matching operations, etc.In some examples, the time stamper 410 may generate relatively coarsetime intervals such as, for example, one second increments, each ofwhich may correspond to an absolute time or a relative time based onsome reference time. However, as described in greater detail below, timestamps and, thus, the time stamper 410, are not necessary to performsignature comparisons, correlations and the like.

The signature generators 406 and 408 provide respective collections ofsignatures or signature information 412 and 414 to a signaturecomparator 416. The signature comparator 416 compares the signatureinformation 412 associated with or generated from the signal 404 to thesignature information 414, which is associated with or generated fromone or both of the signals 210 and 214. As noted above, the signal 404contains audio information associated with the audio/video content(e.g., the channel, program, etc.) currently selected by the audio/videocontent selector 402 from the audio/video content signal 203, and thesignals 210 and 214 contain audio information associated with theaudio/video content currently being consumed via the output device 202(FIG. 2).

The comparison of audio signatures or information can be performed usingany known or desired technique. In one example, the signature comparator416 calculates a sum of differences between the reference signatureinformation 412 and the signature information associated with theaudio/video content currently being consumed (i.e., the signatureinformation 414) over a predetermined interval or time period. If thesum of differences is less than or equal to a predetermined threshold,the signature comparator 416 may provide an output signal or information418 indicating that at least a substantial match has been detected(i.e., that the known audio/video content currently selected by theaudio/video content selector 402 is substantially similar or identicalto the audio/video content currently being consumed via the outputdevice 202 (FIG. 2)).

In another example, the signature comparator 416 calculates a differencesignal or an error signal and then calculates an average error, a peakor maximum error, a standard deviation of error, or any other parameterscharacteristic of the differences, if any, between the signatureinformation 412 and 414. One or more of those parameters orcharacteristics may be compared to one or more threshold values and adetermination of whether a substantial match or an identical matchexists is indicated via the output 418 based on whether those parametersor characteristics are less than or greater than one or more of thethreshold values.

In another example explained in detail in connection with FIGS. 10-14,the signature comparator 416 may calculate index values from elements ofthe signature information 414 and use the index values to access adatabase containing audio/video content information and/or the referencesignature information 412. The database may also have time stamp dataassociated with each entry in the database. The signature comparator 416may query the database using the index values and calculate a histogramof query results, which may be used by the signature comparator 416 todetermine whether a substantial match exists.

The signature comparator 416 may also provide a feedback signal orinformation 420 to the audio/video content selector 402 to facilitatethe selection of audio/video content (e.g., channels, programs, etc.)from the reference audio/video content signal 203. For example, in theevent that the signature comparator 416 determines that the signatureinformation 412 and 414 are not substantially similar or identical(i.e., the audio/video content currently selected or tuned from thereference or audio/video content signal 203 by the audio/video contentselector 402 does not substantially match the audio/video contentcurrently being consumed via the output device 202 (FIG. 2)), thefeedback signal 420 may indicate a non-match condition to theaudio/video content selector 402. In turn, the audio/video contentselector 402 may select or tune the next portion of audio/video content(e.g., a next channel or program) in its audio/video content search orscan sequence.

An audio/video content identifier 424 is coupled to the audio signaturecomparator 416 and receives the match information output 418. If theaudio/video content identifier 424 receives information (via the output418) indicating that a substantial or identical match has beenidentified, the audio/video content identifier 424 determines theidentity of the audio/video content currently being consumed via theoutput device 202 (FIG. 2). More specifically, the audio/video contentcurrently being consumed via the output device 202 (FIG. 2) may beidentified as a particular broadcast channel, program, website, etc.

The audio/video content identifier 424 is coupled to the site unit 218(FIG. 2) and provides the audio/video content identification informationto the site unit 218 (FIG. 2) via the communication link 220. The siteunit 218 may use the audio/video content identification informationprovided by the audio/video content identifier 424 to generateconsumption records and the like.

FIG. 5 is a flow diagram that generally depicts an example manner inwhich the audio signature processor 400 shown in FIG. 4 may beconfigured to collect or generate and process audio signatures.Initially, the signature generators 406 and 408 (FIG. 4) collect orgenerate signatures and send the signatures to the signature comparator416 (FIG. 4) (block 502). As described in greater detail in connectionwith FIG. 7 below, the signature collection or generation process (block502) may use the characteristics of audio features such as, for example,temporal characteristics such as the times between zero crossings, thetimes between peak values crossing a predetermined threshold, the timevarying spectral characteristics of an audio signal, etc. Regardless ofthe particular media signal characteristics and features that are usedto collect or generate signatures or signature information, thesignature comparator 416 compares signature information received fromthe signature generator 406 to signature information received from thesignature generator 408 (block 504).

There are many well-known methods to compare signatures. One knownsignature comparison method may use a byte by byte comparison.Alternatively, signatures may be compared within a specific number ofbits (e.g., three bits) of error. As described in greater detail belowin connection with FIG. 8, an audio signal may be divided into aplurality of successive time intervals, each of which may be an equal orunequal number of seconds, minutes, etc. Signatures may be generatedwithin the confines of these time intervals or sampling periods tofacilitate efficient matching of signatures. For example, one signatureper second may be generated. In such a case, a matching algorithm couldmatch a reference signal signature (e.g., a signature derived from theaudio/video content signal 203 (FIG. 4)) generated within a timeinterval (e.g., a one second interval) to a consumption signal (e.g.,one or both of the signals 210 and 214) signature generated within thatsame time interval. Alternatively or additionally, the signaturematching algorithm could match the reference signal signature generatedwithin a predetermined time interval to signatures generated for one orboth of the consumption signals 210 and 214 (FIG. 4) over a plurality oftime intervals.

Regardless of the particular signature matching technique employed bythe signature comparator 416 (FIG. 4), if the signature comparator 416(FIG. 4) determines that a signature received from the signaturegenerator 406 (FIG. 4) matches (either substantially or identically) asignature received from the signature generator 408 (FIG. 4) (block508), the signature comparator 416 conveys the matching information 418to the audio/video content identifier 424 (FIG. 4). In turn, theaudio/video content identifier 424 identifies the audio/video content(e.g., the channel, program, etc.) to which the audio/video contentselector 402 (FIG. 4) is currently tuned and, thus, the audio/videocontent currently being consumed via the output device 202 (FIG. 2)(block 510). For example, if the signature comparator 416 (FIG. 4) andthe audio/video content identifier 424 (FIG. 4) are implemented usingseparate processor-based systems, the signature comparator 416 (FIG. 4)may convey an interrupt to the audio/video content identifier 424 (FIG.4). Alternatively, if the signature comparator 416 and the audio/videocontent identifier 424 are implemented within the same processor-basedsystem, a software function call may be used to indicate to theaudio/video content identifier 424 (FIG. 4) that a matching conditionhas occurred within the signature comparator 416 (FIG. 4). After theaudio/video content has been identified (block 510), the audio/videocontent identifier 424 (FIG. 4) sends the signatures or signatureinformation along with any other desired audio/video contentidentification information (e.g., program identifiers, time stamps,etc.) to the site unit 218 (FIG. 2) via the communication link orconnection 220 (FIG. 2) (block 512).

On the other hand, if at block 508 the signature comparator 416 (FIG. 4)determines that a signature received from the signature generator 406(FIG. 4) does not match a signature received from the signaturegenerator 408 (FIG. 4), the signature comparator 416 (FIG. 4) transferscontrol to block 514 to invoke an audio/video content selection process,which is described in greater detail in connection with FIG. 6. Afterthe audio/video content selector 402 (FIG. 4) performs the audio/videocontent selection process at block 514, control returns to block 502, atwhich the signature generators 406 and 408 (FIG. 4) again generatesignature information or signatures.

FIG. 6 is a flow diagram that depicts an example manner in which theaudio/video content selector 402 shown in FIG. 4 may be configured toperform the audio/video content selection function described inconnection with block 514 of FIG. 5. Initially, the audio/video contentselector 402 (FIG. 4) identifies all audio/video content portions (e.g.,channels, programs, etc.) that have not yet been compared to thesignal(s) (e.g., the signals 210 and 214) that are associated with theaudio/video content currently being consumed via the output device 202(FIG. 2) (block 602). If the audio/video content selector 402 (FIG. 4)determines that the reference audio/video content signal 203 containsaudio/video content that has not yet been compared to the consumptionsignal 210, 214 (block 604), the audio/video content selector 402 (FIG.4) selects another portion of audio/video content (e.g., tunes toanother broadcast channel or program) (block 606) and then returnscontrol or ends (block 610). The audio/video content selector 402 (FIG.4) may, for example, determine if broadcast channels exist that have notyet provided audio/video content for comparison to the consumptionsignal (e.g., the signals 210 and 214) by scanning or searching a seriesof broadcast channels in a predetermined sequence. If the audio/videocontent selector 402 determines at block 604 that all of the audio/videocontent supplied on each of the available broadcast channels has alreadybeen compared to the audio/video content currently being consumed (e.g.,the signals 210 and 214), the audio/video content selector 402 (FIG. 4)may perform one or more error handling techniques (block 608) and thenreturn control or end (block 610).

FIG. 7 is a flow diagram that depicts an example manner in which thesignature generators 406 and 408 of FIG. 4 may be configured to performthe signature generation functions described in connection with block502 of FIG. 5. Initially, the signature generators 406 and 408 obtainsignals associated with audio/video content from a plurality ofaudio/video content sources (block 702). In particular, the signaturegenerator 406 (FIG. 4) obtains the signal 404 (FIG. 4), which containsaudio/video content selected by the audio/video content selector 402(FIG. 4) from the reference audio/video content signal 203 (FIG. 4). Thesignature generator 408 (FIG. 4) obtains one or both of the signals 210and 214, each of which contains audio/video content associated withaudio/video content currently being consumed via the output device 202(FIG. 2). Upon obtaining the signals (block 702), the signaturegenerators 406 and 408 (FIG. 4) identify particular audio features fromtheir respective signals (block 704). For example, the audio features ofinterest may be peak signal values exceeding or falling below apredetermined threshold value, zero crossings, wavelet energies, or anyother time domain (i.e. temporal) or frequency domain (i.e., spectral)feature of an audio signal. The audio features may have variabletemporal characteristics that are substantially uniquely characteristicof the content of that signal, thereby enabling substantially uniquesignatures to be generated therefrom.

After the audio features of interest have been identified at block 704,the signature generators 406 and 408 (FIG. 4) calculate the timeintervals between the audio features (block 706). For example, in thecase where the audio features of interest are peak signal values above apredetermined threshold value, the time intervals are the times betweenthose peak signal values that exceed the predetermined threshold value.The signature generators 406 and 408 use their respective time intervals(calculated at block 706) to generate signatures (block 708).

Following generation of the signatures (block 708), the signalgenerators 406 and 408 (FIG. 4) send their respective signatures to theaudio signature comparator 416 (FIG. 4) (block 710). More specifically,the signature generator 406 (FIG. 4) sends the signatures it generatesto the signature comparator 416 (FIG. 4) via the signal 412 (FIG. 4). Ina similar manner, the signature generator 408 (FIG. 4) sends thesignatures it generates to the audio signature comparator 416 via thesignal 414 (FIG. 4). The signature generators 406 and 408 (FIG. 4) thenend or return control (block 712).

FIG. 8 is a graph that depicts an example audio signal 802 that may beprocessed by the signature generators 406 and 408 shown in FIG. 4. Thesignal 802 includes a plurality of peaks 806, 808 and 810 above athreshold 811, a plurality of peaks (e.g., peaks 812 and 824) below thethreshold 811, and a plurality of zero crossings, two of which areindicated at reference numerals 814 and 816.

When identifying audio features of interest at block 704 of FIG. 7, thesignature generators 406 and 408 (FIG. 4) may identify the peaks 806 and808 within a first time interval or sampling that extends from time t₀to t₁. Likewise the peak 810 may be identified as an audio feature ofinterest within a second or subsequent time interval extending from t₁to t₂. Then, when calculating the time intervals between audio featuresat block 706 of FIG. 7, the signature generators 406 and 408 (FIG. 4)may calculate a time interval 820 between the peaks 806 and 808 for thefirst time interval from t₀ to t₁ and may determine that there are aninsufficient number of peaks exceeding the threshold 811 during thesecond or subsequent time interval running from t₁ to t₂ to enable thecalculation of a peak to peak time interval for the second time interval(t₁−t₂). Time intervals having an insufficient number of peaks mayinstead be assigned a default value of, for example, zero. In thismanner, the signature generators 406 and 408 may generate a series oftime values (e.g., times between peak values above a threshold value)and may use such a series of time intervals to form a signature orsignature information at block 708 of FIG. 7.

Of course, many other techniques may be employed to collect or generatesignatures. For example, the signal features of interest may include aplurality of peaks below the threshold 811 and the time intervalsbetween those peaks may be used to generate the signatures. Stillfurther, the times between zero crossings may be used to generatesignatures. For example, zero crossings 814 and 816 form a time interval822, which may be one of a plurality of zero crossing time intervalsfalling within the time interval between t₀ and t₁. Such multiple timeintervals within the time interval from t₀ to t₁ may be summed,averaged, used to compute a key value (e.g., a hash value) associatedwith a hash table, or mathematically combined in any other manner togenerate a single value for the sampling interval t₀ to t₁. In a similarmanner, a plurality of zero crossing time intervals within the samplinginterval t₁ to t₂ may be mathematically combined. A series of suchmathematically combined values (i.e., values for the sampling intervals)may thereby form a signature for the signal 802.

FIG. 9 is a block diagram that depicts another example manner in whichthe audio signature processor 208 shown in FIG. 2 may be implemented.The example audio signature processor 900 is a processor-based systemthat includes a processor 902 coupled to a memory 904 having software,firmware and/or any other machine readable instructions 916 storedthereon. The processor 902 executes the software, firmware and/ormachine readable instructions 916 to implement substantially the samesignature generation, signature comparison and audio/video contentidentification functions described herein.

The processor 902 may be any suitable microprocessor, microcontroller orprocessing unit capable of executing machine readable instructions. Thememory 904 may be any desired combination of volatile and non-volatilememory including, for example, read-only memory (ROM) devices,electrically erasable programmable read only memory (EEPROM) devices,random access memory (RAM) devices, mass storage devices (e.g., diskdrives for magnetic or optical media), or any other suitable storagedevices.

The example audio signature processor 900 may also include anaudio/video content selector 906, which may be substantially similar oridentical to the audio/video content selector 402 (FIG. 4) that receivesthe reference signal 203. The audio/video content selector 906 iscontrolled by the processor 902 to scan for audio/video content (e.g., aseries of broadcast channels or programs) in a predetermined sequence.As described above in connection with the audio/video content selector402 (FIG. 4), the channel selection sequence may be based on one or morefactors such as, for example, the frequency with which channels aretypically consumed, the most recently consumed channels, etc. Theaudio/video content selector 906 outputs a signal 908 that containsaudio information about a single selected portion of audio/video content(e.g., a program).

Signal conditioning circuitry 910 receives the signal 908 and one orboth of the signals 210 and 214. The signal conditioning circuitry 910may include analog and or digital circuitry for filtering (e.g., noisefiltering, anti-aliasing filtering, transient filtering, 300 Hz to 3000Hz bandpass filtering, etc.), protection circuitry (e.g., surgeprotection circuitry), level shifting circuitry, amplificationcircuitry, attenuation circuitry, or any other known or desired signalconditioning circuitry.

An analog-to-digital (A/D) converter 912 receives the audio programsignals output by the signal conditioning circuitry 910. The A/Dconverter 912 includes at least two channels to enable the simultaneousanalog-to-digital conversion of the conditioned versions of thereference channel signal 908 and the consumption signal (i.e., one orboth of the signals 210 and 214).

The audio signature processor 900 also includes a communicationsinterface 914 that enables the processor 902 to communicate with thesite unit 218 (FIG. 2) via communication link or connection 220 (FIG.2). For example, the communications interface 914 may include levelshifting circuitry, bus line or signal line driver circuitry, or anyother known or desired communications circuitry.

FIG. 10 is a block diagram that depicts another example manner in whichthe signature generators 406 and 408 shown in FIG. 4 may be implemented.The example signature generator 1000 shown in FIG. 10 receives an inputsignal 1001 (which may, for example, correspond to the signal 404 outputby the audio/video content selector 402 and/or the consumption signals210 and 214) via signal conditioning circuitry 1002. The signalconditioning circuitry 1002 may include analog and or digital circuitryfor filtering (e.g., noise filtering, anti-aliasing filtering, transientfiltering, etc.) One particularly useful filtering circuit may provide abandpass filter characteristic from 300 Hz to 3000 Hz. Additionally oralternatively, the signal conditioning circuitry 1002 may includeprotection circuitry (e.g., surge protection circuitry), level shiftingcircuitry, amplification circuitry, attenuation circuitry, or any otherknown or desired signal conditioning circuitry. Of course, the signalconditioning circuitry 1002 may be eliminated from the signaturegenerator 1000 in the event that the signals provided to the signaturegenerator 1000 do not require conditioning.

Conditioned signal(s) 1004 output by the signal conditioning circuitry1002 are provided to a zero crossing detector 1006 and a peak detector1008. The zero crossing detector 1006 may use a one-shot multi-vibratoror the like to output a pulse to the peak detector 1008 each time a zerocrossing occurs within the conditioned signal(s) 1004. The peak detector1008 may be implemented using any desired peak detection circuit todetect peak signal magnitude. For example, in the case where the signals1004 are analog signals, a diode, capacitor and bleed resistorcombination may be used to detect peak value. On the other hand, in thecase where the signals 1004 are digital values, the peak detector 1008may simply retain the largest numerical value following a reset. Thepeak detector 1008 resets (e.g., to zero) in response to zero crossingpulses or other signals provided by the zero crossing detector 1006. Asa result, the peak detector 1008 outputs a series of signal peakmagnitudes, each of which occurs between successive zero crossings.

A summer 1010 receives the series of peak signal magnitudes from thepeak detector 1008 and generates sums of these peak signal magnitudesfor each of the predetermined time intervals or sample intervals. In oneexample, the summer 1010 may sum a plurality of peak magnitudes(absolute values) occurring within a predetermined number of samples(e.g., 125 samples) collected at a predetermined rate (e.g., 8000samples per second) from the conditioned signal 1004. However, othersample sizes and sample rates may be used instead to suit the needs of aparticular application. An output 1014 of the summer 1010 provides aseries of positive sum values at a rate equal to the sample rate dividedby the sample size for each sum. Thus, in the example where the samplerate is 8000 samples/second and the sample size per sum is 125, theoutput 1014 provides sums at a rate of 64 per second. Additionally, asdepicted in FIG. 10, the summer 1010 may also receive a signal 1012(e.g., time stamp values) from the time stamper 410 (FIG. 4) thatenables the summer 1010 to associated time stamp values with one or moreof the sums at the output 1014.

The signature generator 1000 may also include a smoother 1016 thatperforms a smoothing function on the series of sums output by the summer1010 (e.g., weighted zero crossing data). For example, the smoother 1016may perform a low pass filter function to eliminate noise and otherspurious interference or signal components that may adversely affectsignature match detection. One particularly useful smoothing functionmay be based on the formula y(t)=a*x(t)+b*y(t−1), where y represents thesmoothed data, x represents the sum data provided at the output 1014,and a+b=1. Preferably, a=b=0.5. However, a and b may be different valuesif desired to suit the needs of a particular application. A smoothingfunction such as the example function set forth above may besuccessively applied to the data multiple times (e.g., ten times) toachieve a desired smoothness.

The filtering performed by the smoother 1016 may be implemented usingany desired combination of passive components (i.e., resistors,capacitors, inductors, etc.), active components (i.e., transistors,operational amplifiers, etc.) and/or digital components (i.e., digitallogic, processing units, memory, etc.). There are many well-known analogand numerical (i.e., digital) filtering techniques that may be used toimplement the smoother 1016 and, thus, such implementation details arenot discussed in greater detail herein.

The signature generator 1018 may also include a N-tuple generator 1018configured to receive the smoothed data (e.g., weighted zero crossingdata) from the smoother 1016 and form a plurality of N-tuples from thesmoothed data. The N-tuples may be of any size as determined by softwareand/or user input. The N-tuple generator 1018 may analyze the smootheddata and determine maxima points (e.g., peaks) in the data and a timedifference between successive maxima. The N-tuple generator 1018 mayform a plurality of N-tuples using the time differences between maximapoints (e.g., delta times) and associate a time stamp with each N-tuple.For example, if the N-tuple generator 1018 determines the delta timesare {t1, t2, t3, t4, t5, t6} and the N-tuple generator 1018 isconfigured to form 4-tuples, three 4-tuples are formed (e.g., {t1, t2,t3, t4}, {t2, t3, t4, t5}, and {t3, t4, t5, t6}). A person of ordinaryskill in the art will readily appreciate that there are differentmethods to form N-tuples from the set of delta times. As shown in theabove example, one method may use a sliding window that moves over thedelta times and results in overlapping values between the 4-tuples(e.g., the delta times t2, t3, t4 are in the two of the 4-tuples. Othermethods may result in sequential non-overlapping N-tuples.

FIG. 11 is a flow diagram depicting an example process 1100 by which thesignature generator 1000 of FIG. 10 may generate signatures. The exampleprocess 1100 begins by obtaining signals associated with audio/videocontent from a plurality of audio/video content sources (block 1102). Inparticular, the signature generator 1000 obtains signals from the signalinput 1001 (FIG. 10) which may be derived directly or indirectly fromthe reference audio/video content signal 404 (FIG. 4) and/or from theconsumption signals 210 and 214. After the signals associated withaudio/video content have been received (block 1102), the example process1100 calculates smoothed data (e.g., weighted zero crossing data) fromthe signal (block 1104).

FIG. 12 is a flow diagram that depicts an example manner by which thesignature generator 1000 shown in FIG. 10 may be configured to performthe data smoothing function described in connection with block 1104 ofFIG. 11. Initially, the signature generator 1000 resets a sampleinterval sum to zero (block 1200) and then waits for a zero crossing ofthe audio signal for which a signature is to be generated (e.g., theoutput device audio output signal 210 and/or the signal 214) (block1202). Upon detection of a zero crossing (block 1202), the signaturegenerator 1000 continuously or periodically acquires the peak magnitudeof the signal (block 1204) until a subsequent zero crossing is detected(block 1206). After the subsequent zero crossing is detected (block1206), the signature generator 1000 adds the peak magnitude acquired atblock 1204 to an interval sum (block 1208). The signature generator 1000then determines if the sample interval has expired (e.g., apredetermined amount of time has elapsed, a predetermined number ofsamples have been acquired, etc.) (block 1210). The sample interval maybe a predetermined amount of time during which peak magnitudes aresummed. If the sample interval has not expired (block 1210), thesignature generator 1000 returns control to block 1204. On the otherhand, if the sample interval has expired, the signature generator 1000sends the current interval sum to a smoothing function (block 1212) andthen returns control to block 1106 of FIG. 11. Referring back to FIG.11, after the smoothed data has been calculated (block 1104), the audiosignature generator 1000 determines maxima points in smoothed data(e.g., weighted zero crossing data) and the delta times (block 1106).

FIG. 13 is an example graph depicting smoothed data. The delta timesassociated with the smoothed data are calculated and recorded in atable, a list, or some other data structure. For example, the timedifference between a first peak and a second peak (e.g., t1) iscalculated and stored. Next, the time difference between the second peakand a third peak is calculated (e.g., t2) and stored. This processcontinues until all peaks in the smoothed data (e.g., weighted zerocrossing data) are analyzed and the delta times have been calculated andstored.

Again referring to FIG. 11, after the delta times have been calculated(block 1106), the signature generator 1000 forms a plurality of N-tuples(e.g., a set of N objects) from the list of delta-times. For example, ifthe set of delta-times calculated for the smoothed data shown in FIG. 13is {t1, t2, t3, t4, t5}, two sets of 4-tuples may be formed {t1, t2, t3,t4} and {t2, t3, t4, t5}. The number of elements in the N-tuple (e.g.the value of N) may be selected by analyzing performance constraints androbustness of the signature comparator 416 (FIG. 4) and/or centralprocessing facility 124 (FIG. 1). A signature, composed of the pluralityof N-tuples, is formed. The signature may then be transmitted to thesignature comparator 416 (FIG. 4) or to the central processing facility124 (FIG. 1) for analysis (block 1108).

FIG. 14 is a flow diagram depicting an example manner in which thecentral processing facility 124 of FIG. 1 and/or the signaturecomparator 416 of FIG. 4 may be configured to match a signature to abroadcast program. For ease of discussion, the following discussionrefers to the central processing facility 124. However, the processdepicted in FIG. 14 may instead or additionally be performed by thecentral processing facility 124 may be replaced with the signaturecomparator 416 or another device configured to determine the programfrom which one or more signatures originated.

The central processing facility 124 receives the signature composed ofN-tuples (block 1402). The central processing facility 124 may beginprocessing each N-tuple as it is received. The central processingfacility 124 may receive all the N-tuples before attempting to determinethe source of the signature. The signatures collected or generated at amonitored site (e.g., the monitored site 110 (FIG. 1)) and/or asignature comparator (e.g., the signature comparator 416 (FIG. 4)) maycontain noise and, as a result, each value in an N-tuple may be offset(e.g., increased or decreased) before being analyzed to compensate forthe noise. In particular, the signature comparator 416 may be configuredto increase some values in an N-tuple by one. For example, if an N-tuplereceived at the signature comparator 416 is equal to {t1, t2, t3}, a newN-tuple may be generated containing the offset values {t1+1, t2, t3+1}.However, all values of the N-tuple may be offset to form a new N-tupleand the example described above is merely one example implementation.The central processing facility 124 may be configured to use an offsetvalue of one but may also be configured to skip the offsetting of thevalues of the N-tuple.

As each N-tuple is received, a key value (e.g., a hash value) isgenerated for the N-tuple (block 1404). The key value may be calculatedfrom the values of the elements that compose the N-tuple and may be usedto index into a data structure such as, for example, a hash table. Forexample, the key value associated with the elements of the N-tuple(e.g., {t1, t2, t3, t4}) may be calculated as shown below.

key value(t1,t2,t3,t4)=t4+prime*t3+t2*primê2+t1*primê3

The value of prime may be any prime number such as 31. However, thereare many different methods to calculate a key value based on theelements of an N-tuple and the sum of the elements of the N-tupledescribed above is merely one example. In any event, the hash tablecontains program information, reference signatures, and/or any otherinformation that may be used to match the signature to known audio/videocontent such as, for example, a broadcast program. The contents of thehash table may be filled and/or updated by the reference site processor122 (FIG. 1) and/or the signature generator 406 (FIG. 4).

After the key value is calculated (block 1404), the central processingfacility 124 uses the key value to query a hash table containing programinformation and time stamp data associated with the program information(block 1406). A person of ordinary skill in the art will readilyappreciate that a query into a hash table (e.g., in the course ofmatching signatures or an audio/video content identification process)may return multiple results (e.g., result in a collision) depending onthe method used to calculate the key value. Thus, a list of queryresults containing the program information and the associated time stampdata is generated for each query and is stored by the central processingfacility 124 (block 1408).

The central processing facility 124 may also process the results beforestoring the list (block 1408). Each of the signatures received by thecentral processing facility 124 is generated using a group of N-tuples,each of which may have a different time stamp. If the time stamp of anN-tuple is not equal to the time stamp of the first N-tuple received,the time stamps of the results returned by the hash table may beadjusted by the difference between the time stamp of the first N-tupleand the N-tuple currently being analyzed. For example, if the time stampof the first N-tuple is equal to 10:18:02 and the time stamp of thesecond N-tuple is equal to 10:18:03, a correction of −1 second is madeto the list of results returned by the hash table. The list of resultsreturned by the hash table is adjusted and/or corrected so the resultsfrom the hash table are grouped correctly. In the example above, if thelist of results is not adjusted, the resulting histogram will containtwo values (e.g., 10:18:02 and 10:18:03) instead of the one value (e.g.,10:18:02). The central processing facility 124 determines if there areany remaining N-tuples to be processed (block 1410). If N-tuples remain,control returns to block 1404 and a key value is calculated for the nextN-tuple.

Otherwise, a histogram is generated from the lists of query resultsstored by the central processing facility 124 (block 1412). Thehistogram is analyzed and the central processing facility 124 determinesthe most frequently occurring value in the histogram (block 1414). Thecentral processing facility 124 may analyze the number of occurrencesand/or frequency of the most frequently occurring value and compare thenumber of occurrences and/or frequency to a predetermined threshold. Ifthe frequency of the most frequently occurring value is larger than apredetermined threshold, the most frequently occurring value isdetermined to be a match (block 1414). Otherwise, no match is found.

Although certain example audio signature apparatus and methods have beendescribed herein, the functional blocks making up these examples can beimplemented using any desired combination of analog and/or digitalhardware. Further, some or all of these functional blocks may beimplemented within a processor-based system, such as that shown in FIG.9 that executes machine readable instructions or programs, which may beembodied in software stored on a tangible medium such as a CD-ROM, afloppy disk, a hard drive, a digital versatile disk, or a memory. Stillfurther, some or all of the functional blocks may be combined orintegrated together and/or implemented using multiple functional blocks.

Although certain methods, apparatus and articles of manufacture havebeen described herein, the scope of coverage of this patent is notlimited thereto. To the contrary, this patent covers all embodimentsincluding apparatus, methods and articles of manufacture fairly fallingwithin the scope of the appended claims, either literally or under thedoctrine of equivalents.

1. A method of metering consumption of audio/video content, comprising:receiving a signature associated with audio/video content presented at amonitored site, wherein the signature is based on a plurality of timeintervals associated with audio features of the audio/video contentpresented at the monitored site; and identifying the audio/video contentpresented at the monitored site based on the received signature.
 2. Amethod as defined in claim 1, wherein the audio features of theaudio/video content include at least one of peak values and zerocrossings.
 3. A method as defined in claim 1, wherein identifying theaudio/video content presented at the monitored site based on thereceived signatures includes comparing a reference signature associatedwith a reference signal to the signature associated with the audio/videocontent presented at the monitored site.
 4. A method as defined in claim1, wherein the audio/video content presented at the monitored site isdelivered via at least one of a broadcast station and a localaudio/video content delivery device.
 5. A method as defined in claim 1,further comprising generating the signature based on the plurality oftime intervals associated with the audio features of the audio/videocontent presented at the monitored site.
 6. A method as defined in claim5, further comprising filtering the audio/video content prior togenerating the signature.
 7. A method as defined in claim 6, wherein thefiltering uses a low-pass filter.
 8. An apparatus for meteringconsumption of audio/video content, comprising: a memory; and aprocessor coupled to the memory and programmed to: receive a signatureassociated with audio/video content presented at a monitored site,wherein the signature is based on a plurality of time intervalsassociated with audio features of the audio/video content presented atthe monitored site; and identify the audio/video content presented atthe monitored site based on the received signature.
 9. An apparatus asdefined in claim 8, wherein the audio features of the audio/videocontent include at least one of peak values and zero crossings.
 10. Anapparatus as defined in claim 8, wherein the processor is programmed toidentify the audio/video content presented at the monitored site basedon the received signature by comparing a reference signature associatedwith a reference signal to the signature associated with the audio/videocontent presented at the monitored site.
 11. An apparatus as defined inclaim 8, wherein the audio/video content presented at the monitored siteis delivered via at least one of a broadcast station and a localaudio/video content delivery device.
 12. An apparatus as defined inclaim 8, wherein the processor is further programmed to generate thesignature based on the plurality of time intervals associated with theaudio features of the audio/video content presented at the monitoredsite.
 13. An apparatus as defined in claim 12, wherein the processor isfurther to filter the audio/video content prior to generating thesignature.
 14. An apparatus as defined in claim 13, wherein thefiltering uses a low-pass filter.
 15. A machine readable medium havinginstructions stored thereon that, when executed, cause a machine to:receive signature associated with audio/video content presented at amonitored site, wherein the signature is based on a plurality of timeintervals associated with audio features of the audio/video contentpresented at the monitored site; and identify the audio/video contentpresented at the monitored site based on the received signature.
 16. Amachine readable medium as defined in claim 15, wherein the audiofeatures of the audio/video content include at least one of peak valuesand zero crossings.
 17. A machine readable medium as defined in claim15, wherein the instructions, when executed, cause the machine to meterthe audio/video content presented at the monitored site based on thereceived signature by comparing a reference signature associated with areference signal to the signature associated with the audio/videocontent presented at the monitored site.
 18. A machine readable mediumas defined in claim 15, wherein the instructions further cause themachine to generate the signature based on the plurality of timeintervals associated with the audio features of the audio/video contentpresented at the monitored site.
 19. A machine readable medium asdefined in claim 18, wherein the instructions further cause the machineto filter the audio/video content prior to generating the signature. 20.A machine readable medium as defined in claim 19, wherein the filteringuses a low-pass filter.